Hey Umberto,
I've seen some topics on this about 2-3 years ago. So what I say might be a little out of date.
As an example, say I'm departing/arriving at a random airport in Europe and I'd like to have ground servicing by Wisag, Menzies, or Swissport.
When I edit the parking spot in GSX, I just have to enter Wisag, MENZ, Swissport in the airline parking code box, right? (Also is there still any "weight" to which one is selected)
Topics from a few years ago suggest the info is in the sim.cfg for any GSX vehicle. I can easily find the cfg, but none of the ones I looked at have it.
I'm just making the assumption that the code to enter for a specific handler matches the name of the "texture.***" folder now? Is that right?
Thanks,
Rob